Background: Ovarian cancer is a highly lethal gynaecological malignancy with over 240,000 new cases and 190,000 deaths annually worldwide. Breastfeeding has been proposed as a protective factor through ovulation suppression and hormonal modulation, but the specific impact of breastfeeding duration on ovarian cancer risk requires updated synthesis of recent evidence. Objective: To systematically review and synthesise evidence from the last five years on the association between breastfeeding duration and the risk of ovarian cancer. Methods: A systematic review was conducted following PRISMA 2020 guidelines. PubMed/MEDLINE and Scopus were searched from January 2021 to January 2026 for studies reporting quantitative measures of association (hazard ratios, odds ratios, relative risks) between breastfeeding duration and ovarian cancer incidence. Two independent reviewers performed screening using Rayyan. Risk of bias was assessed using the ROBINS-I tool. Due to potential sample overlap, a narrative synthesis was performed. Results: Of 137 records screened, two large nationwide Korean cohort studies met inclusion criteria, encompassing 2,285,774 women (Kim JH et al., 2026) and 3,754,906 postmenopausal women (Kim LY et al., 2026). Both studies defined prolonged breastfeeding as ≥12 months. Kim JH et al., reported a significant risk reduction among premenopausal women (hazard ratio 0.86, 95% confidence interval 0.77–0.96), while no significant association was observed in postmenopausal women within that study. Kim LY et al., stated a reduced risk for postmenopausal women with ≥12 months of breastfeeding, though the exact hazard ratio was not provided in the abstract. Risk of bias was moderate for both studies, primarily due to potential residual confounding and recall bias. Conclusions: Breastfeeding for 12 months or longer is associated with a clinically meaningful reduction in ovarian cancer risk, particularly among premenopausal women. These findings support breastfeeding promotion as a low-cost, effective primary prevention strategy. Future research should include diverse populations and detailed duration categories to refine dose-response estimates.